Laser pumping of thyristors for fast high current rise-times

ABSTRACT

An optically triggered semiconductor switch includes an anode metallization layer; a cathode metallization layer; a semiconductor between the anode metallization layer and the cathode metallization layer and a photon source. The semiconductor includes at least four layers of alternating doping in the form P-N-P-N, in which an outer layer adjacent to the anode metallization layer forms an anode and an outer layer adjacent the cathode metallization layer forms a cathode and in which the anode metallization layer has a window pattern of optically transparent material exposing the anode layer to light. The photon source emits light having a wavelength, with the light from the photon source being configured to match the window pattern of the anode metallization layer.

REFERENCE TO RELATED APPLICATIONS

This application claims one or more inventions which were disclosed inProvisional Application No. 61/347,126 filed May 21, 2010, entitled“Laser Pumping of 5 kV Silicon Thyristors for Fast High CurrentRise-Times”. The benefit under 35 USC §119(e) of the United Statesprovisional application is hereby claimed, and the aforementionedapplication is hereby incorporated herein by reference.

ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

This invention was made with Government support under Grant No.DE-FG-02-08ER85188, awarded by the Department of Energy. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to the field of switches for pulsed powerapplications. More particularly, the invention pertains to switches forpulsed power applications requiring high voltage blocking, high currentdensity, compact size, low cost, high reliability, high efficiency, andfast current rise times.

2. Description of Related Art

Current commercial technology provides many semiconductor devices forswitch applications. These include but are not limited to thyristors,such as the gate turn-off (GTO), metal-oxide-semiconductor gated(MOS-Gated) thyristor, and integrated gate-commutated thyristor (IGCT),and transistors, such as the insulated gate bipolar transistor (IGBT)and the metal-oxide-semiconductor field-effect transistor (MOSFET). Someof these devices have very fast turn-on times, very low resistance, orhigh voltage blocking capabilities. But none of them have the parametersrequired for some pulsed power applications, such as the ability toachieve 5 kV blocking, 5 kA peak with a turn-on time of less than 50 ns,and an on-state resistance less than 10 mΩ, at a reliability and pricesuitable for sale in the commercial market.

A device with the lowest on-state resistance and highest current densityis a thyristor. The thyristor is basically a four layer device havingalternating doping structure in the form P-N-P-N. The first P isconnected to the anode metal and the last N is connected to the cathodemetal. Typically the second P is connected to the gate metal for silicon(Si) devices. For asymmetric devices, those which block only in onedirection, the first N is the only thick layer.

The turn-on time of the device, when electrically controlled, is limitedby the thickness of the layers, the shape of the gate structure, and thegate current. The thickness of the layers determines the transit time ofthe charge carriers which directly impacts the turn-on time. The greaterlength of the gate-cathode region per active area, the faster the turnon time. The interdigitated structure can achieve meters of gate-cathodelength per cm² of active area, which is several orders of magnitudebetter than more common involute structures. These properties have beenmaximized in devices like the Solidtron, a GTO type thyristor, fromSilicon Power Incorporated. The result is a device with a turn-on timegreater than 200 ns. A slower device results in increased turn-on losseswhich means lower switching efficiency and higher thermal load.

Faster devices are being developed in two areas. One area is concernedwith trying to develop faster devices with improved efficiency in powertransmission or conversion. This area needs faster devices to reduce theturn-on losses, which become the more dominant loss factor as theon-state resistances have become very low. These devices can operate atvery high frequency and average current, but have low peak currents.

The second area, to which this invention is applicable, is concernedwith low-frequency, high-peak power applications. These applicationsinclude military defense, medical, and research fields. More specificexamples could be radar, radiation therapy, or particle accelerators.

Based on the need for faster devices, much work is being directed towardcreating switches for pulsed power applications. Some of that workinvolves using silicon carbide (SiC), gallium nitride (GaN), or othermaterials that can handle higher electric fields and therefore wouldhave inherently faster operation. However these devices have very longdevelopment times and also high cost compared to standard Si devices.Many advances have been made with silicon devices improving turn-on timesuch as using highly interdigitated gate structures, laser triggering,and modified structures. One further method for improving turn-on timeis optical pumping such as described by U.S. Pat. No. 4,207,583.

Laser pumping uses photons to generate charge carriers in asemiconductor device. Because of the regenerative properties ofthyristors, once sufficient charge carriers are generated, theregenerative action will maintain sufficient charge carriers to conductthe current at the on-state resistance. So, optical pumping can allow asemiconductor device to turn-on as fast as the charge carriers can bephoto-generated, rather than waiting for those charge carriers to beinjected from the base region as is required for electrically oroptically triggered semiconductor devices.

A limitation with laser pumping has been the cost and size of therequired laser source. Previously solid state or gas lasers operating inthe infrared (IR) range were used. These types of lasers are large andcostly and were only usable in installation having sufficient space andresources. To be able to commercialize the devices, high-power,low-cost, pulsed, compact laser diode arrays needed to be developed.Normally laser diodes operate in or near continuous-wave (CW) operationat low peak power for applications like fiber-optic communication. Also,previously laser diodes were not produced with wavelengths appropriatefor laser pumping Si thyristors.

Other attempts at laser pumped devices used thick silicon which is not acommercial material. Thick silicon also makes it harder to optimize thedistribution of charge carriers throughout the device, as there is animbalance between absorption and photon energy. If the laser wavelengthis too long then the energy is below the band-gap and the photon cannotefficiently generate charge carriers. If the wavelength is too shortthen all of the light is absorbed in a thin layer and the chargecarriers are not photo-generated throughout the device.

SUMMARY OF THE INVENTION

The present invention uses multiple stages of laser pumpedsemiconductors in series, based on a thyristor or equivalent designhaving regenerative charge carrier properties. The semiconductor andlaser being specifically designed for optimum performance resulting in<50 ns current rise times.

In one embodiment, an optically triggered semiconductor switch includesan anode metallization layer; a cathode metallization layer; asemiconductor between the anode metallization layer and the cathodemetallization layer and a photon source. The semiconductor includes atleast four layers of alternating doping in the form P-N-P-N, in which anouter layer adjacent to the anode metallization layer forms an anode andan outer layer adjacent the cathode metallization layer forms a cathodeand in which the anode metallization layer has a window pattern ofoptically transparent material exposing the anode layer to light. Thephoton source emits light having a wavelength, with the light from thephoton source being configured to match the window pattern of the anodemetallization layer.

In another embodiment, an multi-stage optically triggered semiconductorswitch, includes a plurality of stages coupled in series, eachcomprising: an anode metallization layer; a cathode metallization layer;a semiconductor between the anode metallization layer and the cathodemetallization layer, comprising at least four layers of alternatingdoping in the form P-N-P-N, in which an outer layer adjacent to theanode metallization layer forms an anode and an outer layer adjacent thecathode metallization layer forms a cathode and in which the anodemetallization layer has a window pattern of optically transparentmaterial exposing the anode layer to light and a photon source emittinglight having a wavelength, the light emitted from the photon sourcebeing configured to match the window pattern of the anode metallizationlayer.

Alternatively, the cathode metallization layer may have the windowpattern of optically transparent material exposing the cathodemetallization layer to light and the photon source emits light having awavelength, with the light from the photon source is configured to matchthe window pattern of the cathode metallization layer.

In another embodiment, both the cathode metallization layer and theanode metallization layer each have the window pattern of opticallytransparent material exposing the cathode metallization layer and theanode metallization layer to light and the photon source emits lighthaving a wavelength, with the light from the photon source is configuredto match the window pattern of the cathode metallization layer and theanode metallization layer.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic of an optically gated switch device of anembodiment of the present invention.

FIG. 2 shows a doping profile of the N and P regions of a four layeredoptically gated switch device of an embodiment of the present inventionwith windows in the anode side, cut along line 2-2 of FIG. 3.

FIG. 3 shows a top down view of an anode side of an optically gatedswitch device of an embodiment of the present invention.

FIG. 4 shows a mask layout defining the optically gated switch devicemetallization for wafer with forty five optically gated switch devices.

FIG. 5 shows is an anode side of an optically gated switch device of anembodiment of the present invention.

FIG. 6 shows a laser diode source of an embodiment of the presentinvention.

FIG. 7 shows a graph of relative anode resistance versus wavelength.

FIG. 8 shows a graph of switch current versus time, comparing electricaltriggering to optical triggering of the same device.

FIG. 9 shows a graph of load current versus time at a range of currentlevels.

FIG. 10 shows a graph of load current and laser diode current versustime.

FIG. 11 a shows a schematic of a horizontal configuration of opticallygated switch devices of an embodiment of the present invention, witheach optically gated switch device with a separate laser diode array.

FIG. 11 b shows a schematic of a vertical stack configuration ofoptically gated switch devices of an embodiment of the presentinvention, with each optically gated switch device with a separate laserdiode array.

FIG. 11 c shows a schematic of a horizontal configuration of opticallygated switch devices of an embodiment of the present invention, with asingle laser diode connected to an optical waveguide to provide opticalcharging to all of the optically gated switch devices.

FIG. 12 shows a doping profile of the N and P regions of a four layeredoptically gated switch device of an alternate embodiment of the presentinvention with windows in the cathode side of the device.

FIG. 13 shows a doping profile of the N and P regions of a four layeredoptically gated switch device of another embodiment of the presentinvention with windows in both the anode side and cathode side of thedevice.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic of an optically gated switch device or switchof an embodiment of the present invention. In the first embodiment, thephoton source 1 is a laser diode array. The photons 2 travel from thephoton source 1 to the thyristor 3 of the optically gated switch device.The photon source 1 can be located coplanar to the thyristor 3 or therecan be some separation between the photon source 1 and the thyristor 3.In an alternate embodiment the photons 2 from the photon source 1 maytravel through waveguides or fiber-optic cables from the photon source 1to the thyristor 3.

The photons 2 enter through a surface of the thyristor 3 throughoptically flat openings or windows 6 patterned through the anodemetallization 4 of the thyristor 3. The photons 2 will generate chargecarriers (not shown) throughout the full thickness of the thyristor 3.Opposite the anode metallization 4 of the thyristor 3 is the cathodemetallization 5. An external anode connection would be made to the anodemetallization 4 and an external cathode connection would be made to thecathode metallization 5. Optical drive power would be provided throughconnections 7 at the photon source 1.

FIG. 2 shows an example of a doping profile of the N and P regions of alayered optically gated switch device of an embodiment of the presentinvention cut along line 2-2 of FIG. 3. In one embodiment, commercialtechniques are used to process silicon 660 μm thick, neutrontransmutation doped, 750 Ω-cm, N-type silicon. This material has beenwell developed and reliable with very low manufacturing costs. Thinhighly doped layers are then created using standard commercialtechniques.

As well as lower manufacturing costs, the use of relatively thinsemiconductor wafers results in a more efficient switch. For example, a20 kV switch composed of four, 5 kV switches connected in series willresult in lower switching and conduction losses than a 20 kV switchfabricated from a single thick device.

The structure includes a cathode metallization 5, a cathode region 10 ofN+ conductivity material, cathode shorts 11 of P+ conductivity material,a base region 12 of P− conductivity material, a drift region 13 of N−conductivity material, a buffer region 14 of N conductivity material, ananode region 15 of P+ conductivity material, an anode metallization 4,optically flat openings or windows 6 through the anode metallization 4,and anode shorts 16 of N+ conductivity material.

Above the anode metallization 4 and the opening 6 is an anode region 15with thinner large area shorts 16. These large area shorts 16 dischargethe first P-N junction. The anode region 15 may for example have adoping level of 1.0×10²⁵ m⁻³, with a depth of 0.75 μm and doped inboron. The shorts 16 may for example have a doping level of 1.0×10²⁵m⁻³, with a depth of 0.5 μm and doped in phosphorus.

Below the cathode metallization 5 is a cathode region 10 with large areashorts 11 and a buried base region 12. The large area shorts 11 on thecathode side discharge a second P-N junction. The cathode region 10 mayfor example have a doping level of 1.0×10²⁶ m⁻³, with a depth of 0.5 μmand doped in phosphorus. The shorts 11 may for example have a dopinglevel of 1.0×10²⁵ m⁻³, with a depth of 0.6 μm and doped in boron. Thebase region 12 may for example have a doping level of 3.3×10²² m⁻³, witha depth of 6 μm and doped in boron.

Below the base region 12 is a drift region 13, which may for examplehave a doping level of 1.0×10¹⁹ m⁻³, with a depth of 650 μm. Below thedrift region 13, is a buffer 14, which may for example have a dopinglevel of 6.0×10²² m⁻³ and a depth of 6 μm and doped in phosphorus.

The central N-P junction, between the base region 12 and the driftregion 13 requires the charge to recombine which will limit the turn-offtime of the device. Also on the cathode side are junction terminationextensions 24 to grade the voltage across the surface of the devicerather than across the thickness of the device. This allows the electricfield outside of the device to be much lower than the field inside thedevice reducing the stress on the insulating material packaging thedevice.

Alternatively, the optically gated switch device may include four layerdevices fabricated in other materials such as SiC and gallium arsenide(GaAs). Three layer devices can also be used, but require constantillumination to keep the devices in the on state.

Reverse conduction is an essential requirement for high power solidstate switches. Most pulsed power systems will have load faults whichresults in reverse current. It is important that the switch survivethese events as they typically represent a substantial portion of thesystem cost, and in causes where faults are self healing, it is oftenessential that the system operation is not interrupted.

While diodes can be used to control reverse current, they add to thecost and complexity of the system and do not completely prevent theswitch from seeing reverse current because of the finite inductance ofthe connections between diode and switch and the turn-on and turn-offtime for the diode. Therefore, it is desirable that the switches be ableto conduct reverse current. Furthermore, designing the switch to becapable of conducting the full reverse current eliminates the need toadd diodes.

One example of the optically flat openings 6 through the anodemetallization 4 is shown in FIG. 3. The smaller neck 20 expands to alarger base 21 for the metallization remaining between openings 6. Theouter edge 22 of the openings 6 is kept within the inner edge 23 of thecathode metallization 5 on the opposite side of the device as thisdefines the active area of the device. The area outside of the cathodemetallization 5 on the cathode side, opposite the side shown in FIG. 3,of the device is the junction termination region 24 which grades thevoltage across the top surface of the device rather than the thicknessof the device allowing the device package to have lower electric fieldstress outside of the silicon.

In one embodiment, the openings 6 are preferably optically flat windowspatterned through the anode metallization 4 of the optically gatedswitch device. The outer edge of the window pattern 22 would beequivalent to the inner edge of the junction termination region 25. Thisallows for the most metal contact on the cathode side which isrestricted by the junction termination extension 24. The design openingpattern or window pattern takes into account the lateral resistance ofthe P type layer on the anode side. If the openings are too large thenthe current density will cause localized over-heating in that regionwhich will damage the device. Making that layer thicker or lessresistive in the same thickness actually increase the turn-on time orincrease the amount of photons absorbed in that region which is notdesired. Therefore, window pattern should expose as much as possible,while not being too large that the over-heating occurs.

In one embodiment, for example, the window pattern may have thefollowing measurements, with the widest portion of the windows 6 being0.25 mm apart at the neck 20, with the windows 6 closest to the outeredge 23 being 10.50 mm high and 2.75 mm wide at the middle portion ofthe window. The remaining windows 6 are 10.5 mm tall, 1.25 mm wide atthe top and bottom portions and 2.81 mm wide at the middle portion ofthe window.

In an alternate embodiment, the openings 6 are preferably optically flatwindows patterned through the cathode metallization 5 of the opticallygated switch device as shown in FIG. 12, rather than through the anodemetallization 4 as shown in FIGS. 2 and 3 and discussed above. This hasthe advantage of allowing the entire anode side to be attached to theanode electrode and heat sink resulting in very low thermal impedancefrom device to heat sink. Encapsulation of the device to protect thetermination region must accommodate the cathode-side window.

In another embodiment, the openings 6 are preferably optically flatwindows patterned through the cathode metallization 5 and the anodemetallization 4 of the optically gated switch device as shown in FIG.13. This allows the device to be pumped from either or both sides. Withboth sides of the device having windows, the device can increase theoptical power delivered without having to increase the optical powerdensity.

Additionally, it may be desirable to use anti-reflective coatings toimprove the delivery of the optical energy to the optically gated switchdevice. Also, optical gels and other media can be placed between thephoton source and the optically gated switch device, contacting thesurfaces of both to improve the transfer of optical energy.

The openings 6 or windows in the metallization are designed to maximizethe opening area while maintaining low resistance, low inductanceconnections. This can be accomplished by using metallization patternsthat are narrow in the center of the device where the integrated currentis small, and increase in size toward the edges as the total currentconducted by the electrodes increases. This can be measured by modelingthe current to determine the current density in the electrode at anypoint, therefore determining the required size of the electrode toprevent over heating. Grid designs with constant width conductors arenot optimal, as the conductor width must be sufficient to carry largecurrent densities at the edge of the device, making them much largerthan necessary at its center, resulting in less available window area.Therefore, the required size of the electrode.

FIG. 4 shows an example of a mask pattern for processing the siliconwafer into devices. This mask pattern includes several individual masksincluding the edge of the cathode metallization 5 and the openings 6 inthe anode metallization 4. The pattern on the anode side of an actualdevice can be seen in FIG. 5.

Use of standard silicon wafers allows many devices to be fabricated on asingle wafer with conventional processing techniques and facilities, ascan be seen in FIG. 4. As semiconductor device cost is dominated bywafer processing costs rather than material cost, this design lowers thecost of manufacturing. Because specialized processing is not required,manufacturing costs are further reduced and rapid scale up in volume ispossible.

FIG. 6 shows an example laser diode array used as a photon source 1. Thelaser diode array is patterned to match the window pattern through themetallization on the anode side. In other words, the emitter pattern 30of the photon source 1, in this case the laser diode array matches theopenings 6 in the anode metallization 4 of the optically gated switchdevice. This prevents any of the photons from being reflected by metalon the anode side. The openings 6 or optically flat windows furtherreduce reflections from the interface. Some of the light will not beabsorbed on the first pass and will be reflected by the metal on thecathode side.

For example, for an optically gated switch device that is only 660 μmthick, the transit time of a photon is less than 10 ps, so usingmultiple passes will not affect turn-on time. It is then possible toachieve a high degree of absorption in the device with charge carriersdistributed throughout the thickness of the optically gated switchdevice.

The optimum wavelength for high switch efficiency is determined by boththe number of charge carriers generated and the location of the chargecarriers. FIG. 7 shows a graph of resistance versus wavelength. Assumingall the charge carriers are optically generated, for a 660 μm thicknessoptically gated switch device, optimum results are achieved with awavelength in the range of 1020 nm-1080 nm, since these wavelengthsoffer the small amount of resistance. Slightly shorter wavelengthsresult in greater number of charge carriers, but the distribution acrossthe optically gated switch device varies by more than a factor of ten,resulting in a less efficient switch.

To achieve saturated charge carrier density would require less than 50μJ of such photons creating charge carriers. However, during turn-onsome amount of charge carriers will be generated by thyristor action, sonot all of the charge carriers need to be photo-generated. For example,a 1 kW pulse for 40 ns can achieve 5 kA using an appropriately designedthyristor structure. The energy required to achieve saturated chargecarrier density is small, but creating these charges in a short timerequires a high peak power photon source.

The cost of the photon source is a key driver for the practicalapplication of the optically gated switch device. Four-layer devices candecrease the optical power and energy requirements. In many practicalapplications, the current rise time is limited by external load. Theminimum requirement for the optical power and energy can be determinedfor specific current and rise time requirements by including thyristoraction and the rate at which charge carriers are needed to achieve thedesired rise time and switch efficiency, in the calculation. Thisresults in substantially reduced switch costs. Furthermore, by using afour-layer device optimized for fast turn-on, the optical powerrequirements can be further decreased. Thus, even though the opticallygated switch device is turned on promptly from photo-generated chargecarriers, it is still desirable to optimize the regenerativecharacteristics of the optically gated switch device.

The laser diode array can be integrated to the stage such that there islittle distance between the semiconductor and the laser emitter. Thelaser diode array can then be driven using a compact self-powered driversuch as described in Applicant's U.S. Pat. No. 6,624,684, hereinincorporated by reference.

FIG. 8 shows a graph of switch current versus time comparing optical(see line 40) to electrical (see line 41) triggering of the same device.As is shown, the optical triggering 40 resulted in a significantlyshorter turn-on delay and rise time since optical triggering seeds thewhole optically gated switch device with charge carriers, as opposed tothe electrical triggering 41 which needs to inject the charge carriersfrom the gate region which requires transit times across the opticallygated switch device to generate sufficient charge carriers forconduction.

FIG. 9 shows the effects of peak laser diode current on peak switchdi/dt. At low current, e.g. 1 A, the results are similar to electricaltriggering. At high current, for example 15.5 A, 18 A, and 20 A there isnot much further improvement over 5 A, therefore the power requirementsof the laser diodes can be limited without major impact on performance.

FIG. 10 shows switch performance at 2500 A peak switch current 60 versuslaser diode array current 61, showing that the peak switch current 60lags the laser diode trigger current by less than 5 ns, with the lagtime being between the initial rise of optical power of the laser diodearray current to the initial rise of switch current. Furthermore, theoptical power falls well before the switch current 60 reaches peak,showing that maintaining the optical power on from the laser diode arraycurrent is not required for switch performance after the initial turn-ontime.

FIG. 11 a shows a horizontal configuration of optically gated switchdevices of an embodiment of the present invention, with each opticallygated switch device with a separate photon source 1, preferably an arrayof laser diodes. The array of photon sources 1, are coupled to thethyristors 3 and photons 2 travel from the array of photon sources 1 tothe thyristors 3, which are triggered optically.

The photons 2 enter through a surface of the thyristor 3 throughoptically flat openings 6 patterned through the anode metallization 4 ofthe thyristor 3. The photons 2 will generate charge carriers (not shown)throughout the full thickness of the thyristor 3. Opposite the anodemetallization 4 of the thyristor 3 is the cathode metallization 5. Theexternal anode connection would be made to the anode metallization 4 andthe external cathode connections would be made to the cathodemetallization 5. Optical drive power would be provided throughconnections 7 at the photon source 1. Each of the thyristors 3 arecoupled together with stage to stage connections 8 between the cathodemetallization 5 of one thyristor to the anode metallization 4 of anadjacent thyristor 3.

For series connected stacks, horizontally, as shown in FIG. 11 a orvertically, as shown in FIG. 11 b, each of the thyristors 3 are atdifferent potentials when the optically gated switch device is in an offstate. If the photon sources 1 are at the anode or cathode potential ofeach stage, then their respective power supplies and input controlsignals must be isolated. These separate photon sources can beexternally powered using appropriate high voltage isolation techniquesas known in the art.

Another method providing optically triggering thyristors 3 is to use aself-powered gate drive as described in Applicant's U.S. Pat. No.6,624,684, which is herein incorporated by reference. A self-poweredgate drive uses voltage across the optically gated switch device topower each stage. No other power source is required. The turn-on controlsignal can be applied to each stage via small high voltage (HV)isolation transformers or by using fiber optics or other opticalisolation to trigger a low voltage, low power photo sensitive switch oneach stage. The auto trigger described in Applicant's U.S. Pat. No.7,072,196, hereby incorporated by reference, can also be applied tooptically gated switch device of the present invention, where instead ofdriving the gate of a thyristor the output from the auto triggered gatedrive is connected to the photon source either directly or via aself-powered amplifier.

Alternatively, the photon source 1 may be isolated from the thyristor 3at each stage, so all the photon sources 1 can be at the same potential,eliminating the need for any other HV isolation. The isolation betweenphoton source 1 and thyristor 3 must be sufficient to hold off thelargest potential difference in the optically gated switch device,limiting this approach to a few series connected stages.

For optically gates switch devices with a large number of stages or forsystems using many optically gated switch devices, it may beadvantageous to employ a single light source 110, such as one or morelaser diodes, to drive all stages of all optically gated switch devices111 a-111 c as shown in FIG. 11 c. Light from the light source 110 iscoupled to the stages/thyristors 111 with a light guide 9 comprisingmultiple optical waveguides, light pipes or optical fibers from thesource 110 to each stage 111, such that the output of the waveguides,light pipes or fibers 9 forms the photon source 112 a-112 c for thestage 111 a-111 c. Each of the stages 111 a-111 c are coupled togetherwith stage to stage connections 8 between the cathode metallization 5 ofone stage to the anode metallization 4 of an adjacent stage. The lightsources can be remotely located and can all operate at the samepotential. There is no limit to the number of stages that can beconnected is series or parallel.

Alternate photon sources can be used, such as high power lasers andlight emitting diodes with the same requirements for wavelength, etc asdescribed above. High power sources driving optical waveguides or fiberoptics are advantageous for driving multiple stage switches or fordriving multiple different optically gated switch devices to insureprecise simultaneous turn on. This technique can also be employed toestablish precise timing between different switches by using differentoptical path lengths to each switch.

Accordingly, it is to be understood that the embodiments of theinvention herein described are merely illustrative of the application ofthe principles of the invention. Reference herein to details of theillustrated embodiments is not intended to limit the scope of theclaims, which themselves recite those features regarded as essential tothe invention.

What is claimed is:
 1. An optically triggered semiconductor switchcomprising: a) an anode metallization layer; b) a cathode metallizationlayer; c) a semiconductor between the anode metallization layer and thecathode metallization layer, comprising at least four layers ofalternating doping in a form P-N-P-N, in which an outer layer adjacentto the anode metallization layer forms an anode and an outer layeradjacent the cathode metallization layer forms a cathode; in which theanode metallization layer has a window pattern of optically transparentmaterial exposing the anode layer to light; wherein the window patterncomprises a plurality of windows of transparent material, each windowhaving a top portion with a width, a bottom portion with a width, thetop portion being connected to the bottom portion through a middleportion, wherein a width of the middle portion of the window is greaterthan the width of the top portion and the bottom portion of the window;d) a photon source emitting light having a wavelength, the light emittedfrom the photon source being configured to match the window pattern ofthe anode metallization layer.
 2. The switch of claim 1 in which thephoton source comprises an array of laser diodes located such that lightfrom the laser diodes matches the window pattern of the anodemetallization layer.
 3. The switch of claim 1 in which the photon sourcecomprises at least one laser diode coupled to a light guide havingoutputs matching the window pattern of the anode metallization layer. 4.The switch of claim 1, in which the wavelength of the photon source isselected to achieve an even distribution of photo-generated chargecarriers throughout a thickness of a device.
 5. The switch of claim 1,in which a thickness of the P type layer near the anode side and the Nand P type layers on the cathode side are selected to produce thefastest turn-on times.
 6. A multi-stage optically triggeredsemiconductor switch, comprising a plurality of stages coupled inseries, each comprising: a) an anode metallization layer; b) a cathodemetallization layer; c) a semiconductor between the anode metallizationlayer and the cathode metallization layer, comprising at least fourlayers of alternating doping in a form P-N-P-N, in which an outer layeradjacent to the anode metallization layer forms an anode and an outerlayer adjacent the cathode metallization layer forms a cathode; in whichthe anode metallization layer has a window pattern of opticallytransparent material exposing the anode layer to light wherein thewindow pattern comprises a plurality of windows of transparent material,each window having a top portion with a width, a bottom portion with awidth, the top portion being connected to the bottom portion through amiddle portion, wherein a width of the middle portion of the window isgreater than the width of the top portion and the bottom portion of thewindow; d) a photon source emitting light having a wavelength, the lightemitted from the photon source being configured to match the windowpattern of the anode metallization layer.
 7. The switch of claim 6,wherein the stages are coupled in series and stacked horizontally. 8.The switch of claim 6, wherein the stages are coupled in series andstacked vertically.
 9. The switch of claim 6, in which the photon sourcecomprises an array of laser diodes located such that light from thelaser diodes matches the window pattern of the anode metallization layerfor each of the stages.
 10. The switch of claim 6, in which the photonsource comprises at least one laser diode coupled to a light guidehaving outputs matching the window pattern of the anode metallizationlayer of each of the stages.
 11. An optically triggered semiconductorswitch comprising: a) an anode metallization layer; b) a cathodemetallization layer; c) a semiconductor between the anode metallizationlayer and the cathode metallization layer, comprising at least fourlayers of alternating doping in a form P-N-P-N, in which an outer layeradjacent to the anode metallization layer forms an anode and an outerlayer adjacent the cathode metallization layer forms a cathode; in whichthe cathode metallization layer has a window pattern of opticallytransparent material exposing the cathode metallization layer to lightwherein the window pattern comprises a plurality of windows oftransparent material, each window having a top portion with a width, abottom portion with a width, the top portion being connected to thebottom portion through a middle portion, wherein a width of the middleportion of the window is greater than the width of the top portion andthe bottom portion of the window; d) a photon source emitting lighthaving a wavelength, the light emitted from the photon source beingconfigured to match the window pattern of the cathode metallizationlayer.
 12. The switch of claim 11 in which the photon source comprisesan array of laser diodes located such that light from the laser diodesmatches the window pattern of the cathode metallization layer.
 13. Theswitch of claim 11 in which the photon source comprises at least onelaser diode coupled to a light guide having outputs matching the windowpattern of the cathode metallization layer.
 14. The switch of claim 11,in which the wavelength of the photon source is selected to achieve aneven distribution of photo-generated charge carriers throughout athickness of a device.
 15. An optically triggered semiconductor switchcomprising: a) an anode metallization layer; b) a cathode metallizationlayer; c) a semiconductor between the anode metallization layer and thecathode metallization layer, comprising at least four layers ofalternating doping in a form P-N-P-N, in which an outer layer adjacentto the anode metallization layer forms an anode and an outer layeradjacent the cathode metallization layer forms a cathode; in which thecathode metallization layer and the anode metallization layer each havea window pattern of optically transparent material exposing the anodemetallization layer and the cathode metallization layer to light whereinthe window pattern comprises a plurality of windows of transparentmaterial, each window having a top portion with a width, a bottomportion with a width, the top portion being connected to the bottomportion through a middle portion, wherein a width of the middle portionof the window is greater than the width of the top portion and thebottom portion of the window; d) a photon source emitting light having awavelength, the light emitted from the photon source being configured tomatch the window pattern of the cathode metallization layer and theanode metallization layer.
 16. The switch of claim 15 in which thephoton source comprises an array of laser diodes located such that lightfrom the laser diodes matches the window pattern of the anodemetallization layer and the cathode metallization layer.
 17. The switchof claim 15 in which the photon source comprises at least one laserdiode coupled to a light guide having outputs matching the windowpattern of the anode metallization layer and the cathode metallizationlayer.
 18. The switch of claim 15, in which the wavelength of the photonsource is selected to achieve an even distribution of photo-generatedcharge carriers throughout a thickness of a device.
 19. A multi-stageoptically triggered semiconductor switch, comprising a plurality ofstages coupled in series, each comprising: a) an anode metallizationlayer; b) a cathode metallization layer; c) a semiconductor between theanode metallization layer and the cathode metallization layer,comprising at least four layers of alternating doping in a form P-N-P-N,in which an outer layer adjacent to the anode metallization layer formsan anode and an outer layer adjacent the cathode metallization layerforms a cathode; in which the anode metallization layer and the cathodemetallization layer each have a window pattern of optically transparentmaterial exposing the cathode metallization layer and the anodemetallization layer to light wherein the window pattern comprises aplurality of windows of transparent material, each window having a topportion with a width, a bottom portion with a width, the top portionbeing connected to the bottom portion through a middle portion, whereina width of the middle portion of the window is greater than the width ofthe top portion and the bottom portion of the window; d) a photon sourceemitting light having a wavelength, the light emitted from the photonsource being configured to match the window pattern of the anodemetallization layer and the cathode metallization layer.
 20. The switchof claim 19, wherein the stages are coupled in series and stackedhorizontally.
 21. The switch of claim 19, wherein the stages are coupledin series and stacked vertically.
 22. The switch of claim 19, in whichthe photon source comprises an array of laser diodes located such thatlight from the laser diodes matches the window pattern of the anodemetallization layer and the cathode metallization layer for each of thestages.
 23. The switch of claim 19, in which the photon source comprisesat least one laser diode coupled to a light guide having outputsmatching the window pattern of the anode metallization layer and thecathode metallization layer of each of the stages.